A former senior manager at Bunnings has pleased guilty to taking secret kickbacks from an insurance company in return for steering the DIY chain's business its way.

Christopher David Green, 66, today pleaded guilty today at the Auckland District Court to breaching the 103-year-old Secret Commissions Act. He admitted he corruptly received and retained secret commissions totalling approximately $142,000 for referring insurance business to HIG between 2003 and 2010.

As a result, his employer was consequently over-charged by a sum of about $220,000 for that insurance.

Green, whose activities were revealed in June, was employed by Bunnings as a commercial property manager where his role included ensuring the portfolio of premises that his employer occupied around New Zealand, were appropriately insured.

Herbert Insurance Group is now in the hands of liquidators and its founder Grant Herbert, who has been bankrupted, is facing multiple charges laid by the SFO.

Acting SFO chief executive, Simon McArley, said everyone loses when commercial corruption, in the form of kick-backs, occurs.

"It distorts the market causing otherwise competitive companies to lose business and results in higher prices for consumers. Our levels of corruption are seen to be relatively low in New Zealand, but there is still further work to be done to stamp out what is an insidious practice."

The Secret Commissions Act was passed into law in 1910 and the penalties reflect that.

Businesses convicted face fines of up to $2000, while an individual faces fines of up to $1,000 and up to two years in jail.